U.S. patent number 4,294,020 [Application Number 06/148,517] was granted by the patent office on 1981-10-13 for plenum drying hopper with integral heaters.
This patent grant is currently assigned to Whitlock, Inc.. Invention is credited to Arthur J. Evans.
United States Patent |
4,294,020 |
Evans |
October 13, 1981 |
Plenum drying hopper with integral heaters
Abstract
A plenum drying hopper for granular material includes a housing
enclosing a plenum chamber, an upper material inlet for introducing
a flow of granular material into the plenum chamber, and a
perforate diffuser cone, located in the lower portion of the plenum
chamber, that directs the granular material from the plenum chamber
into a material outlet. The perforations in the diffuser cone are
large enough to permit ready passage of gas therethrough but small
enough to preclude passage of all but the finest particles of the
granular material. A gas inlet extends into the lower portion of
the housing for introducing a drying gas (air) into the plenum
chamber; a gas outlet discharges the gas from the upper part of the
housing. Heaters are provided for heating the gas prior to its
entry into the plenum chamber. The improvement comprises a
deflection shield structure mounted in the housing below the plenum
chamber between the heaters and the diffuser cone, that directs
heated air along a labyrinthine path from the heaters through the
diffuser cone and into the plenum chamber. It also shields the
diffuser cone from the heaters to prevent radiant heat from
reaching the diffuser cone, and deflects fine particles of the
granular material that pass through the diffuser cone directly into
the material outlet.
Inventors: |
Evans; Arthur J. (Northville,
MI) |
Assignee: |
Whitlock, Inc. (Farmington,
MI)
|
Family
ID: |
22526109 |
Appl.
No.: |
06/148,517 |
Filed: |
May 9, 1980 |
Current U.S.
Class: |
34/168; 34/169;
34/226 |
Current CPC
Class: |
F26B
17/14 (20130101) |
Current International
Class: |
F26B
17/12 (20060101); F26B 17/14 (20060101); F26B
017/14 () |
Field of
Search: |
;34/168,169,174,226,231
;219/374,381 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schwartz; Larry I.
Attorney, Agent or Firm: Kinzer, Plyer, Dorn &
McEachran
Claims
I claim:
1. A plenum drying hopper for reducing the moisture content of
granular material, comprising:
a housing enclosing a plenum chamber and including an upper
material inlet for introducing a flow of granular material into the
plenum chamber and a lower material outlet for discharging the
granular material from the plenum chamber;
a perforate diffuser cone, at the bottom of the plenum chamber, for
directing the flow of granular material from the plenum chamber
into the material outlet, the perforations in the diffuser cone
being large enough to permit ready passage of gas therethrough and
small enough to preclude passage of all but the finest particles of
the granular material;
a gas inlet, extending into the housing below the diffuser cone,
for introducing dry gas into the plenum chamber through the
diffuser cone;
a gas outlet, extending from the upper portion of the housing, for
discharging gas from the housing after contact with the granular
material flowing through the plenum chamber;
a separator barrier positioned between the gas inlet and the
diffuser cone;
a plurality of gas passages extending through the separator
barrier;
a plurality of heaters, one in each gas passage, for heating gas
flowing from the gas inlet through such passages toward the
diffuser cone; and
deflection shield means, mounted in the lower portion of the
housing, between the heaters and the diffuser cone, for deflecting
heated gas along a labyrinthine path from the heaters into the
plenum chamber through the diffuser cone, shielding the diffuser
cone from the heaters to prevent radiant heat from reaching the
diffuser cone and deflecting any fine particles of the granular
material that pass through the diffuser cone into the material
outlet.
2. A plenum drying hopper according to claim 1 in which the
deflector means comprises two imperforate conical shield members
which converge toward the lower material outlet, the two shield
members being spaced apart to provide a portion of the labyrinthine
path for the heated gas.
3. A plenum drying hopper according to claim 1 or claim 2 in which
each gas passage through the separator barrier comprises a tube
enclosing one of the heaters.
4. A plenum drying hopper according to claim 3 in which each heater
is an electrical resistance heater.
Description
BACKGROUND OF THE INVENTION
This invention relates to plenum drying hoppers for granular resin
materials used in plastic molding and similar processing. More
particularly, the invention concerns a plenum drying hopper which
uses relatively high temperature heaters in the hopper itself in a
construction that precludes melting of the granular material,
especially fine particles of that material.
The need for higher operating temperatures in plenum drying hoppers
has long been recognized, but problems have existed due to melting
of the granular plastic materials, especially the fine particles or
dust from these materials, when high temperature heaters are used.
For other granular materials, radiant heat from high-temperature
heaters may damage the material without actual melting. Another
problem has existed in that fine particles which pass through the
diffuser screen may fall on the heaters and must be cleaned out
from the bottom of the hopper. Any fine particles or dust that
falls on the heaters is likely to melt and hence is not easily
removable, creating a difficult clean-up problem.
SUMMARY OF THE INVENTION
It is an object of the invention, therefore, to provide a new and
improved plenum drying hopper for granular material, using high
temperature heaters located within the hopper, that effectively
precludes any melting or other damage to the granular material from
radiant heat produced by the heaters.
Another object of the invention is to provide a new and improved
plenum drying hopper for granular material that effectively
precludes loss of fine material through the diffuser cone employed
to introduce a drying gas (air) into the plenum chamber of the
hopper, returning the fine material to the outlet of the
hopper.
Accordingly, the invention relates to a plenum drying hopper for
reducing the moisture content of granular material that includes a
housing enclosing a plenum chamber. The plenum chamber has an upper
material inlet for introducing a flow of granular material into the
plenum chamber, a lower material outlet for discharging the
granular material from the plenum chamber, and a perforate diffuser
cone at the bottom of the plenum chamber for directing the flow of
granular material from the plenum chamber into the material outlet.
The perforations in the diffuser cone are large enough to permit
ready passage of gas therethrough yet are small enough to preclude
the passage of all but the finest particles of the granular
material. A gas inlet extends into the housing, below the diffuser
cone, for introducing dry gas into the plenum chamber. A gas outlet
extends from the upper portion of the housing for discharging gas
from the housing after contact with the granular material flowing
through the plenum chamber. A separator barrier is positioned
between the gas inlet and the diffuser cone, and a plurality of
heaters are mounted in gas passages extending through that barrier
to heat gas flowing from the gas inlet through those passages
toward the diffuser cone. Deflection shield means are located in
the lower portion of the housing, between the heaters and the
diffuser cone. The deflection shield means directs heated gas along
a labyrinthine path from the heaters into the plenum chamber
through the diffuser cone while shielding the diffuser cone from
the heaters to prevent radiant heat from reaching the diffuser
cone; the shield also deflects any fine particles of the granular
material that passed through the diffuser cone to the material
outlet.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevation view, with parts broken away and partially
in cross section, of a plenum drying hopper constructed in
accordance with a preferred embodiment of the invention; and
FIG. 2 is a plan view of the heater elements and separator plate of
the plenum drying hopper of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a plenum drying hopper 10 connected to a dehumidifying
dryer 11. Dehumidifier dryer 11 may be of any conventional type
which will reduce the moisture content of a gas, usually air, which
is introduced into dryer 11 through an inlet 11A, producing a drier
gas at the outlet 11B. The dry gas may be warmed or pre-heated as
desired.
Plenum drying hopper 10 is made up of a housing 12 enclosing a
plenum chamber 13. An insulator jacket 33 may encompass part or all
of housing 12. An upper material inlet 14 and a lower material
outlet 15 allow introduction and withdrawal of granular resin
material from the plenum chamber 13. A gas inlet passage 16 extends
into the plenum chamber 13 and introduces a dry gas from the
dehumidifying dryer 11 into plenum chamber 13. A gas outlet 17 is
spaced from the gas inlet passage 16 and discharges gas from plenum
chamber 13 after the gas has passed through the granular material
within the plenum chamber.
In the drawings, the material inlet 14 is shown as a vacuum loader
cover. However, the material inlet means could be of any other
conventional type, such as a manual loader cover. The material to
be dried is introduced into the plenum chamber 13 through material
inlet 14. An air trap cone 19 allows the material to pass
downwardly and fill the chamber but does not allow gas to escape
through the material inlet 14. The material outlet 15 includes a
slide gate 20 which is closed when there is material in the hopper
and is open to allow the material to exit the chamber for use in an
extrusion molding press or other processing equipment with which
hopper 10 is employed. Thus, the entire plenum chamber 13 is filled
with the granular material to be dried. As resin material is
withdrawn through the outlet 15, additional material is added
through the inlet 14, thus maintaining a full plenum chamber
13.
A separator plate 21 is located in the housing 12 between the gas
inlet passage 16 and the plenum chamber 13. The separator plate is
pierced only by a series of tubular gas passages 22 which extend a
considerable distance above and below the separator plate and by a
material passage 23 leading from chamber 13 to the lower material
outlet 15. The material passage 23 is centrally located in the
separator plate 21 and the tubular passages 22, in this case six in
number, are located in a circle surrounding the material passage as
shown in FIG. 2. A looped electrical resistance heater 24 is
installed in each tubular passage to heat the dried air which
enters the housing 12 through the gas inlet passage 16.
In the plenum drying hopper 10, the drying air or other drying gas
flows upwardly through the tubular heating passages 22 and into an
air diffuser cone 26. The cone 26 is made of a material having a
multiplicity of small openings 34 which allows the gas to diffuse
into the plenum chamber but do not allow the bulk of the granular
resin material to pass through the cone. However, a limited
quantity of fine particles or dust from the granular plastic
material is likely to pass through the openings in the diffuser
cone 26.
To prevent these fine particles or dust from reaching the
electrical resistance heaters 24, a deflection shield means 28 is
installed between the diffuser cone 26 and the tubular passages 22.
The deflector shield means includes an upper imperforate member 29
of truncated conical configuration which extends from the housing
12 downwardly and inwardly toward the central material passage 23,
and a lower imperforate member 30, again of conical configuration,
positioned below member 29. This construction defines a passage 31
between the two conical members 29 and 30. A similar passage 32
separates member 29 and the diffuser cone 26.
The lower end of the conical member 30 is mounted on and sealed to
the exterior of the material passage 23. A portion 23A of the
material conduit 23 is open to the passage 32. Thus, any fine
granulated material or dust which passes through the diffuser cone
26 is directed to the discharge outlet 15 through the inter-cone
passage 32 and the discharge passage 23 and does not come in
contact with the heater elements 24. The positioning of the conical
members 29 and 30 provides a labyrinthine-like passage 31, 32 which
draws heated air from the heaters 24 in a downwardly direction
through the passage 31 and then in an upwardly direction into the
passage 32 and through the diffuser cone 26 as shown by the arrows
in FIG. 1.
The deflection shield means 28 performs two functions. The first is
to prevent radiant heat from the resistance heaters 24 from
impinging directly upon the granular plastic material in the plenum
chamber 13. This precludes melting or other damage to the material
being dried. The second function of shield means 28 is to prevent
any of the dust or finely granulated plastic material from coming
into contact with the high temperature electric resistance heaters
24, which would bring about melting of the plastic dust. Further,
the shield means 28 deflects all dust directly into the outlet
material passage 23, through the open portion 23A, and thus to the
lower material outlet 15 where it becomes a part of the dried
material discharged from the plenum drying hopper 10.
* * * * *